Introducer sheaths are well-known for percutaneous vascular access and typically comprise polytetrafluoroethylene or fluorinated ethylene propylene. These sheaths are of a thin-wall construction, but tend to kink.
Increasing the thickness of the sheath wall minimally improves the level of kink resistance, which is still unacceptable. Sheaths used in hemofiltration and dialysis, in particular, are prone to kinking since they remain positioned in a patient's body for a long time. While positioned in a patient, the sheath may be bent or pinched off and, as a result, kink due to repeated use or patient movement. A kinked sheath is unusable and cannot be straightened while positioned in the body of a patient. Consequently, the sheath must be removed, leaving an enlarged, bleeding opening, which typically cannot be reused. Vascular access is then attempted at an alternative site, and the procedure is restarted. Restarting the procedure causes a time delay, which may be life threatening. In some cases, an alternative site is not available for introducing another sheath.
Another problem with thin-wall sheaths is that an emergency room physician will typically kink an introducer sheath while inserting various catheters therethrough during emergency procedures. Small diameter introducer sheaths are also typically bent and kinked under the time constraints of an emergency situation. As a result, a new sheath must be introduced at the same or another access site.
Another introducer sheath is described in U.S. Pat. Nos. 4,634,432; 4,657,772; and 4,705,511. This introducer sheath utilizes a helical coil spring and a cylindrical wall formed by dipping the spring in a protective coating composition, which completely surrounds the spring. The coating composition comprises a thermoplastic polymer material dissolved in a solvent solution. Although this introducer sheath appears to be more kink-resistant and flexible than a polytetrafluoroethylene sheath, the cylindrical wall is approximately twice as thick as that of the polytetrafluoroethylene sheath with the same inside diameter. The increased outside diameter of this introducer sheath significantly increases the size of the access site, which further accentuates the problem of bleeding.
Introducer sheaths relevant to this delivery catheter are described in U.S. Pat. Nos. 5,380,304 and 5,700,253. These introducer sheaths are flexible and kink-resistant and include typically a flat wire coil having a plurality of uniformly spaced turns positioned and compression fitted around an inner tube. An outer tube is connected to the inner tube through the uniform spacing of the coil turns. As a result, the compression fitted coil reinforces the wall to provide an extremely kink-resistant and thin-walled introducer sheath. Although extremely well suited for its intended purpose of gaining access to, for example, the vascular system, these introducer sheaths are typically of a relatively short length commonly in the neighborhood of eight centimeters, which is ideally suited for gaining vascular access. However, these and other relatively large introducers create large puncture sites, which are more difficult to control bleeding thereat, and do not track as well due to the added stiffness along its entire length.
In order to produce a smaller diameter introducer or catheter, the implantable, self-expanding stents have to be cut from a smaller cannula tube, which resulted in less radial force. Less radial force is thought to be not advantageous, since it is generally believed the higher the radial force of the stent, the better the final treatment will be. Stents cut or formed from smaller tubes or cannula often require the delivery system to have a smaller guide wire lumen, since the stent was being compressed to a smaller diameter. This is thought not to be desirable, since it does not give the support for implantable device positioning like a larger guide wire.
The ZILVER™ stent system of COOK Incorporated, Bloomington, Ind., utilizes a 7 French delivery system which includes a self-expanding stent that has a relatively high radial force compared to other stents in the market place. This stent system utilizes the FLEXOR™ sheath technology disclosed in U.S. Pat. Nos. 5,380,304 and 5,700,253. However, the introducer sheath technology described in these patents has been lengthened to function as a delivery catheter or sheath, which delivers stents over a standard 0.035 inch guide wire. Since this FLEXOR delivery catheter maintains essentially the same wall thickness throughout its length, the distal portion of the delivery catheter maintaining the stent in a compressed state is the limiting factor on reducing the French size (diameter) of the delivery system.